This invention relates to powering of portable electronic devices.
Portable electronic devices generally use a primary battery or a rechargeable battery to provide power. Many devices powered by a primary battery lack a mechanical power switch to turn the device off relying instead on a soft switch, e.g., an electronic switch to turn the device off. Other devices include a mechanical power switch. Those devices that include such a mechanical switch, a user may inadvertently leave the mechanical switch in the “ON” position. Under such circumstances, the device will continue to drain current from the battery and can deeply discharge the battery causing cell venting and electrolyte leakage. Cell venting and electrolyte leakage from the battery can damage the device that houses the battery and are particular problems with alkaline and zinc-carbon cells. In addition, some re-chargeable cells can suffer cell venting and/or electrolyte leakage.
To prevent deep discharge, devices that lack a mechanical switch will use an embedded microcontroller or voltage comparators to operate an electronic switch to switch the device off. While suitable for more expensive devices, these techniques are complex and costly and generally not suitable for inexpensive devices, especially devices that do not already have a need for an embedded microcontroller or voltage comparators for the main function of the device.